The present invention relates to an optical modulation/demodulation system in which optical fibers are used as the signal transmission path.
Conventionally, an optical modulation/demodulation system for transmitting data by means of optical fibers utilizes the modulation of light intensity for converting the bit pattern of the binary data to be transmitted directly into an optical signal by using luminous elements; in other words, it is adapted to supply electric current to a luminous element so as to make it emit light when the binary data to be transmitted is at the level "1" while it makes the element stop emission when the binary data is at the level "0", thereby transmitting data through optical fibers.
In prior art, on the receiving side, it is necessary to convert the optical signal transmitted through the optical fibers into an electric signal, to synchronize various circuits in the receiving side to be operated in the proper order and at chronological intervals and to properly select transmitted data. In order to synchronize various circuits there have been proposed such methods as transmitting a synchronizing signal via a separate transmission line or extracting a clock component from transferred data. Such a method, however, is defective in that the system may involve a complicated structure; especially in the method of extracting a clock component from transferred data, the clock component can not be extracted if the level "0" should continue.
The present invention aims to improve the above mentioned defects and to provide an optical modulation/demodulation system which is capable of transmitting and receiving data either with synchronization or without synchronization with a simple structure. The present invention will now be described in more detail by way of embodiments.